Abstract: The clear stable sols were obtained above 50℃ with about 100:1 suitable H₂O/Al³⁺mol~ ratio, 5:1 ROH/H⁺, 0.07:1 H⁺/Al³⁺ concentrations of
peptizant acid. Crack-free alumina membranes were obtained by rapid gelation processing of sols in shorten gel time. The suitable concentration of the sol was between
0.5～1.4 mol AlOOH/l sol, the suitable spraying distance shorter than 200mm. The pore size of the membrane was influenced by the size of boehmite grain, the pore size
of γ-Al₂O₃ prepared by the boehmite sol with 3 nm grain size was about 3nm. Asymmetric alumina membrane was obtained by further modifying alumina supporter
by using the clear stable sol. When the mean diameter of the colloidal particles was equivalent to the most pore size of the supporter, the crack-free gel film can be
stably deposited on the supporter. With 0.1μm of the most pore size as the supporter, the γ-Al₂O₃ membrane of 3nm pore size was obtained by using the spraying sol of
100nm colloidal particles.

Key words: asymmetric alumina membrane, sol-gel technique, rapid gelation processing